1. Field of the Invention
The present invention relates to a digital mirror device projector using a digital mirror device (hereinafter may be referred simply to as a xe2x80x9cDMDxe2x80x9d) having a plurality of mirror elements and a method of controlling an amount of light being used in the digital mirror device projector, and more particularly to the DMD projector that makes effective use of light being reflected while each of the mirror elements is turned OFF and the method of controlling an amount of light being used in the digital mirror device projector.
2. Description of Related Art
A DMD (Digital Mirror Device) projector is generally known which uses a DMD panel having several hundreds of thousand of mirror elements each being able to control an inclination for being mounted being placed on a semiconductor memory cell and which controls a reflection state by exerting control on the inclination of each of the mirror elements to form an image, which is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 10-78550.
In the disclosed DMD projector, light emitted from a light source is configured to be condensed as a spot on a color wheel, being made up of a plurality of kinds of color filters adapted to selectively let any one of red, green, and blue color light pass and light having passed through any one of the color filters is applied, in a form of a parallel luminous flux, on the DMD panel and image light being light reflected off the DMD panel is projected through a zoom projection lens onto a screen.
As described above, the projector using the DMD forms an image with the reflected light, and brightness of the image is dependent on brightness of the light source. The brightness of the light source varies dependently on an elapsing time and deteriorates gradually after shipment. The projector using the conventional DMD is not considered in this point and has a problem in which an image cannot be projected at constant brightness for a long time, as shown in FIG. 5.
In view of the above, it is an object of the present invention to provide a projector using a DMD for projecting an image at constant brightness usually.
According to a first aspect of the present invention, there is provided a digital mirror device projector including:
a light source being voltage-controllable for an amount of light;
a color wheel configured by combining a plurality of kinds of color filters for making image light of a plurality of colors;
a digital mirror device panel having a plurality of mirror elements each being controlled so as to be put in a first inclination state and in a second inclination state and reflecting light fed from the light source and passed through any one of the color filters making up the color wheel while being put in the first inclination state, as the image light, in a first direction and reflecting light fed from the light source and passed through any one of the color filters making up the color wheel while being put in the second inclination state in a second direction being different from the first direction;
an image controller to control so as to put each of the mirror elements in the first inclination state or the second inclination state according to a gray level signal as a corresponding video signal;
a photoelectric conversion device being placed as a photo-sensor in such a position where the light reflected from at least one of the mirror elements is incident when the at least one of the mirror elements is in the second inclination state and, whereby the photoelectric conversion device receives the reflected light and converts the received light to a voltage;
a reference voltage source to generate a predetermined reference voltage; and
a voltage controller to compare the predetermined reference voltage generated in the reference voltage source with the voltage output from the photoelectric conversion device, and to control the amount of the light fed from the light source, based on a result of the comparison.
In the foregoing first aspect, a preferable mode is one wherein the voltage controller compares the predetermined reference voltage generated in the reference voltage source with the voltage output from the photoelectric conversion device, and to control the amount of the light fed from the light source so that the voltage is matched to the predetermined reference voltage.
Also, a preferable mode is one wherein the color wheel is configured by combining a red color filter, a green color and a blue color filter for making image light of the plurality of colors.
Another preferable mode is one wherein during startup of the digital mirror device projector, the image controller controls so as to put at least one of the mirror elements in the second inclination state, and the voltage controller is configured to control an amount of the light fed from the light source.
Still another preferable mode is one wherein during power-OFF of the digital mirror device projector, the image controller controls so as to put at least one of the mirror elements in the second inclination state, and the voltage controller is configured to control an amount of the light fed from the light source.
A further preferable mode is one wherein during startup of the digital mirror device projector, the image controller controls so as to put all of the mirror elements in the second inclination state, and the voltage controller is configured to control an amount of the light fed from the light source.
A still further preferable mode is one wherein during power-OFF of the digital mirror device projector, the image controller controls so as to put all of the mirror elements in the second inclination state, and the voltage controller is configured to control an amount of the light fed from the light source.
An additional preferable mode is one wherein the image controller outputs a gray level signal to the reference voltage source in addition to the digital mirror device panel, wherein the reference voltage source varies a reference voltage to be generated in accordance with the gray level signal, and whereby during power-ON of the digital mirror device projector, the amount of the light of the light source is controlled by the voltage controller.
According to a second aspect of the present invention, there is provided a light amount control method for controlling an amount of light to be used in a digital mirror device projector made up of a light source being voltage-controllable for an amount of light; a color wheel configured by combining a plurality of kinds of color filters for making image light of a plurality of colors; a digital mirror device panel having a plurality of mirror elements each being controlled so as to be put in a first inclination state and in a second inclination state and reflecting light fed from the light source and passed through any one of the color filters making up the color wheel while being put in the first inclination state, as the image light, in a first direction and reflecting light fed from the light source and passed through any one of the color filters making up the color wheel while being put in the second inclination state in a second direction being different from the first direction; an image controller to control so as to put each of the mirror elements in the first inclination state or the second inclination state according to a gray level signal as a corresponding video signal, the method including:
a placing step of placing a photoelectric conversion device as a photo-sensor in such a position where light reflected from at least one of the mirror elements is incident when the at least one of the mirror elements is in the second inclination state and, whereby the photoelectric conversion device receives the reflected light and converts the received light to a voltage;
a predetermining step of predetermining a reference voltage; and
a controlling step of comparing the predetermined reference voltage with the voltage output from the photoelectric conversion device, and controlling the amount of the light fed from the light source, based on a result of the comparison.
Also, a preferable mode is one wherein, in the controlling step, the amount of the light fed from the light source is controlled so that the voltage is matched to the predetermined reference voltage.
Another preferable mode is one wherein the color wheel is configured by combining a red color filter, a green color and a blue color filter for making image light of the plurality of colors.
Still another preferable mode is one wherein during startup of the digital mirror device projector, an amount of the light fed from the light source is controlled, by having the image controller control so as to put at least one of the mirror elements in the second inclination state.
A further preferable mode is one wherein during power-OFF of the digital mirror device projector, an amount of the light fed from the light source is controlled, by having the image controller control so as to put at least one of the mirror elements in the second inclination state.
A still further preferable mode is one wherein during startup of the digital mirror device projector, an amount of the light fed from the light source is controlled, by having the image controller control so as to put at least one of the mirror elements in the second inclination state.
An additional preferable mode is one wherein during power-OFF of the digital mirror device projector, an amount of the light fed from the light source is controlled, by having the image controller control so as to put at least one of the mirror elements in the second inclination state.
A still additional preferable mode is one wherein the image controller outputs a gray level signal to the reference voltage source in addition to the digital mirror device panel, wherein the reference voltage source varies a reference voltage to be generated in accordance with the gray level signal, and whereby during power-ON of the digital mirror device projector, the amount of the light of the light source is controlled.
With the above configurations, in the projector using the DMD panel, the light irradiated to the DMD panel and the inclination state of each mirror element on the DMD panel are controlled in accordance with the video signal, an angle for reflecting light is changed in the first inclination state and in the second inclination state, the light reflected in the first inclination state advances in the first direction of the screen and a like on which the image is projected, and the light reflected in the second inclination state becomes an electric signal representing a intensity of the light output from the photo-sensor. The voltage of the main power source is changed in accordance with light intensity, thereby projecting the image at a constant brightness always.
The light at a time where the mirror element is turned OFF is used and the intensity of the light is measured to control the power source voltage, thereby achieving the object.
Further, a fixed image is needed to measure the intensity of the light, however, by outputting a specific image pattern for a constant period when the power source is turned OFF, there is no problem.
Also, as to the constant brightness, for example, the power source voltage is set to 80% at shipping and the power source voltage is increased in a manner that brightness of the light source is kept constant, whereby the constant brightness can be kept until the power source voltage becomes maximum.
Additionally, a fixed image is needed when the light intensity is measured. Therefore, for example, a specific image pattern may be output for a constant period at the power-OFF of the DMD projector. Therefore, it is possible to watch images at the constant brightness regardless of brightness variation caused by deterioration of the light source.